Method for analyzing rare earth-activated rare earth oxide and oxysulfide phosphors

ABSTRACT

This disclosure depicts a method for quickly and accurately determining the emission color and activator content of rare earth-activated rare earth oxide and oxysulfide phosphors such as Y2O2S:Eu. The method involves exciting the tested phosphor by ultra-violet irradiation or other suitable stimulation, detecting the intensities of predetermined spectral lines in the emission spectrum of the excited phosphor, and comparing the related intensities of the detected lines to derive an indication of the emission color and activator content of the phosphor.

United States Patent 1 Feb. 19, 1974 Forest METHOD FOR ANALYZING RAREEARTH-ACTIVATED RARE EARTH OXIDE Primary Examiner-Archie R. Borchelt N LPHOSPHORS Attorney, Agent, or Firm-John H. Coult [75] inventor: HarveyForest, Skokie, Ill. [73] Assignee: Zenith Radio Corporation, Chicago,ABSTRACT This disclosure depicts a method for quickly and accu- [22]Filed: Nov. 2, 1972 rately determining the emission color and activatorcontent of rare earth-activated rare earth oxide and I Appl' 303298oxysulfide phosphors such as Y O,S:Eu. The method involves exciting thetested phosphor by ultra-violet [52] U.S. Cl. .7 250/459, 250/61irradiation or other suitable stimulation, detecting the [51] Int. Cl.G0ln 21/38 intensities of predetermined spectral lines in the emis- [58]Field of Search 250/365, 458, 459, 461, 483, sion spectrum of theexcited phosphor, and comparing 250/484 the related intensities of thedetected lines to derive an indication of the emission color andactivator con- [56] References Cited tent of the phosphor.

22 Claims, 2 Drawing Figures METHOD FOR ANALYZING RARE EARTH-ACTIVATEDRARE EARTH OXIDE AND OXYSULFIDE PHOSPHORS BACKGROUND OF THE INVENTIONMakers of color television picture tubes have recently initiated largescale usage of light-emitting phosphors of the rare earth-activated rateearth oxysulfide class. An important example of such a phosphor iseuropium-activated yttrium oxysulfide, a red-emitting phosphor ofincreasing commercial significance. The emission spectra of thesephosphors are characterized by extremely narrow emission lines. Becauseof the high degree of difficulty encountered in ascertaining theemission color of phosphors having narrow emission lines, theintroduction into commercial use of such phosphors has engendered agreat need for fast and accurate methods of determining their emissioncolor.

lt is well known that the emission color and brightness of the Y O S:Euphosphor depends to a high degree upon the concentration of the europiumactivator. The color coordinates on a tristimulus color diagram of Y OS:Eu with different europium concentrations ex-.

hibit the well-known shift of emission color from yellow to red withincreasing europium concentration.

This emission color shift has been attributed to the sequentialquenching of the D D and D emitting states. The emission spectrum of Y OS:Eu consists of many narrow lines from all three of these emittingstates, resulting in a composite emission color. The dominant emissionsfrom B fall in the blue-green region, from D, in the green-yellowregion, and from D in the yellow-red region. Thus, as the D and Demissions are sequentially quenched with increasing europiumconcentration, the emission color becomes progressively more red. Atcommercial europium concentration levels, typically in the order of 3.6mole per cent, the D emissions do not contribute significantly and theemission color of the phosphor is determined primarily by the relativestrengths of the D, and D emissions.

In spite of the strong need for quick, simple and accurate methods ofdetermining the emission color of rate earth-activated rare earthoxysulfide phosphors, there presently exists no practically usefulmethods. Conventional colorimetric techniques involving the use of acombination of a number of wideband filters are not sufficientlyaccurate to analyze narrow-line emitting phosphors.

Due to the lackof a fast and reliable emission color test, manytelevision color tube makers are forced to rely on a subjective visualinspection test. Visual inspection of the emission color of theseoxysulfide phosphors has proven to be unsatisfactory, this method beingextremely subjective, unreliable and prone to errors induced, interalia, by intensity differences in the tested phosphor samples.

A third method which is used in analytical chemical laboratories, butwhich has little practical utility for online factory inspections,involves the use of a sophisticated spectrometer coupled to a computer.The spectrometer scans the entire phosphor emission spectrum andproduces a spectrograph while the computer develops an integratedintensity characteristic of the detected spectrum. For accuratedeterminations the spectrometer-computer is typically set to sample thespectrum through a band-pass approximately 5 angstroms wide. Assuming anemission spectral range for the tested phosphor of 2,000 angstroms ormore, it can be seen that the instrument must take and analyze at least400 samples, a time-consuming and costly operation.

The overall time required to perform the spectrometric-computing methodis due to a great extent to the setup procedures required. Since thespectrometercomputer scans the total emission spectrum of the testedphosphor, the complete spectrum must be free from spectral linesgenerated by foreign sources. A consequence of this constraint is thatthe phosphor to be tested must be excited to emission by a cathode raybombardment under conditions which closely approximate the operatingconditions of a cathode ray tube. Before a color emission test on abatch of phosphor can be performed, the phosphor must be depositedwithin a vacuum bottle and established in a vacuum environment, much asit would be in an assembled color tube, before the test can begin. Thedescribed setup procedures typically consume 3-4 hours or more. Further,whereas the described spectrometer-computer is capable of developingdata which may be useful to the particular laboratory involved, theresults are commonly incapable of being correlated reliably with datataken by different instruments in other laboratories.

In spite of the complexity and cost of the operation, and the relativelygreat time consumption, the results developed by this method are notextremely accurate due to the difficulties which exist in maintainingthe intensity of the phosphor emission constant over the time requiredto scan its emission spectrum.

As may be expected, since there did not exist prior to this invention anaccurate and reliable method susceptible to standardization formeasuring the emission color of rare earth-activated rare earthoxysulfide phosphors, practical problems have developed in the supply ofsuch phosphors by phosphor vendors to the tube makers. Specifications onemission color developed by tube makers often have not been met by thephosphor vendors to the satisfaction of the tube makers.

OBJECTS OF THE INVENTION lt is a general object of this invention toprovide a method for quickly and accurately determining the emissioncolor of rare earth-activated rare earth oxide and oxysulfide phosphors.

it is another object to provide such a method which is repeatable withsimilar results, which is capable of being standardized independently ofspectrometric equipment and laboratory procedures employed, and whichmay be carried out reliably by relatively untrained personnel and withrelatively inexpensive spectrometric equipment.

It is still another object of this invention to provide a method fordetermining with a high degree of accuracy the activator concentrationin a sample of rare earth-activated rare earth oxide or oxysulfidephosphors.

lt is yet another object to provide a method for determining theemission color of or activator concentration of rare earth-activatedrare earth oxide or oxysulfide phosphors which does not requireexcitation by cathode ray bombardment, but which can be performed by theuse of UV (ultra-violet) irradiation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph illustrating theshift in emission color of the emission spectra of europium-activatedyttrium oxysulfide phosphor as the europium concentration is changed;and

FIG. 2 is a calibration curve developed according to the method of thisinvention which illustrates the relationship between line intensityratio and europium concentration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS It is extremely important thatthe emission characteristics of television picture tube phosphors becapable of accurate predetermination, in order that the color contrast,brightness and color balance of the three primary color phosphors beproper. Because of its relatively high luminous efficiency and favorablespectral properties, the rare earth-activated rare earth oxysulfidephosphor, Y O S:Eu, has recently gained widespread use in colortelevision tubes. Other such phosphors may gain commercial acceptance inthe future.

FIG. 1 illustrates, in terms of the x and y coordinates of a C.I.E.(Commission Internationale de IEclairage) color diagram, the variationin the emission color of yttrium oxysulfide (Y O szEu) as a function ofits europium content. In spite of a long felt need, there did not existprior to this invention a quick, accurate and otherwise satisfactorymethod for ascertaining the emission color of Y O S:Eu or other rareearth-activated rare earth oxysulfide phosphors, nor, secondarily, theirconcentration of europium (or other activator).

This invention is directed to a method for determining the emissioncolor of a sample of rare earthactivated rare earth oxysulfide phosphorand/or its activator content, which comprises basically the followingsteps. First, the phosphor is excited to stimulate light emission.Secondly, the intensities of predetermined spectral lines in theemission spectrum of the excited phosphor are detected. Thirdly, therelative intensities of the detected spectral lines are compared toderive an indication of the emission color and/or the activator contentof the phosphor.

In more detail, the tested phosphor is preferably excited by UV(ultra-violet) irradiation. Although the sample may be excited byelectron bombardment, by irradiation with X-rays or high energyradiation, the use of UV irradiation is preferred for reasons ofsimplicity, low cost, and speed and convenience in the testing procedure(described below). For reasons which will become more apparent as thisdiscussion continues, whereas UV stimulation is not possible in certainprior art methods, it may be employed in the method of this inventionsince contamination of the emission spectrum by the spectrum of the UVlamp used to excite the grated over the breadth of the spectral lines ofinterest.

It is an important aspect of the subject method that one or moreselected lines from each ofa plurality suitable emission manifold bedetected for subsequent comparison of relative intensity. Whereas avariety of spectral lines within these manifolds may be selected toimplement the principles of this invention, in the interest ofconserving test time, it is preferable that the selected spectral linesin the chosen emission manifolds be located close together in theemission spectrum of the phosphor.

Secondly, it is important also that the selected lines not beadulterated by spectral lines produced by the source of UV excitation. I

To the end of satisfying these stated criteria, and con sidering thephosphor Y O SzEu, it is preferable that the spectral lines selected forcomparison are the lines associated with the D, F and D F transitions.As a result of the spectral overlap of the D,, and D, emission manifoldswhich characterize the europium activator, the D, F and D,, Ftransitions occur quite close together 9n the spectrum, namely between5,800 A and 5,900 A. Thus to detect lines associated with thesetransitions it is necessary only to scan this very narrow A) band ofwavelengths in the emission spectrum of the phosphor.

Also, the lines associated with the D F, and D F0 transitions aredesirable for their freedom from interference from lines generated by UVlamps and QIB.9il ."-LHfii" qm. hsrh sphqr s st d- The D,, F transitionis unsplit by the crystal field, with the result that this emissionoccurs as a narrow singlet. However, the D, F transition can be resolvedinto several emission lines. In experiments conducted on Y O szEufollowing the method of this invention, a .larrell-Ash 0725 mmonochrometer having a 6 A bandpass was used. This instrument resolvedthe D F transition into two emission lines. Either of these D,

-*"F=, transition lines may be employed to carry out the -method of thisinvention. The two emission lines associated with the D, F trapsitionswere found to occur at approximately 5,865 A and 5,885 A. The B Ftransition was found to occur at approximately 5,830 A.

In a third basic step of the subject method, the relative intensities ofthe spectral lines detected in the chosen emission manifolds arecompared to derive an indication of the emission color and/or theactivator concentration in the phosphor sample. As applied to Y O S'Eu,it is preferred, in the interest of simplicity and ease of testoperations, that the line intensity peak height as a measure of the lineintensity of the D "F emission line be compared with the line intensitypeak height as a measure of the line intensity of either of theabove-described D, F emission lines to develop a line intensity peakheight ratio (hereinafter LIR). It has been found that this LIRcompletely describes the emission color and also the europium content ofthe tested phosphor.

FIG. 2 is a curve illustrating line intensity peak height rations (LIRs)of the D0 F0 line to the 5,865 A Dt :"F emission line of Y2O S:Eu asafunctionof europlum concentration.

Because a ratio of line intensity values is developed as the descriptionof emission color and europium concentration, rather than an absoluteintensity measurement, no corrections for spectral sensitivity of themonochrometer or calibrations need be made at any time since any errorsor shifts introduced in the measurement of peak intensity of one linewill be substantially equal in measurement of the other line, thuscanceling any effect thereof.

FIG. 2 and the operations performed to develop the FIG. 2 curve will notbe discussed in detail. A series of Y O S:Eu phosphor were prepared withvarying Eu concentration from 2.5 to 6 mole per cent by the usual Na COS flux synthesis procedure which directly converts Y O :Eu into Y O2S:Euwith greater than 99 percent ymdfThe ljgFl j, irli fline intefii ty peakheight ratio) was measured as described above and plotted (closedcircles) in FIG. 2 versus europium concentration in mole per cent. Asmooth curve was able to be drawn through the points. Reproducibility ofthe LIR for different samples at the same europium concentration wasfound to be i 3 per cent.

Using the FIG. 2 curve as a working calibration curve, it is a quick andsimple operation to determine quantitatively how close the emissioncolor of a particular sample of europium-activated yttrium oxysulfidephosphor agrees with a standard color. The LlRs of Y O S:Eu phosphorsused by known commercial color tube makers fall generally in the rangeof 1.0 to 1.5, corresponding to europium concentrations in the range ofabout 3 to somewhat less than 4 mole per cent. A useful relationshipbetween LIR and color coordinates (not shown) can be obtained, ifdesired, by combining FIGS. 1 and 2.

The curve in FIG. 2 may also be used as a very accurate analyticalmethod for determining europium concentration in Y O S:Eu phosphors. Theaccuracy of this method of determining europium concentration is about0.05 per cent in the range of 2-6 mole per cent.

It is possible to extend the testable europium concentration range tohigher or lower concentrations.

Thus this invention makes possible the fast and accurate testing of rareearth-activated rare earth oxysulfide and oxide phosphors to determineemission color, and if desired, the tristimulus color coordinatesthereof, and also to determine the concentration level of the rare earthactivator thereof. For the phosphor maker who must be able tomanufacture phosphors to meet given color emission specifications, acalibration curve is preferably made. If the specification is in termsof LIR, a curve as described above and shown in FIG. 2, may be used. Theexact LIR desired can then be predetermined by selection of anappropriate europium concentration level. If a specification of coloremission is made in terms of CIE coordinates, e.g., rather than in LIR,a conversion may be made by the use of a curve such as is shown in FIG.1.

The above-described method has been particularized in connection withanalysis of yttrium oxysulfide phosphors activated by trivalenteuropium. The principles of this invention will apply equally toanalysis ofrare earth-activated rare earth phosphors other than yttriumoxysulfide. A general group of phosphors which may be analyzed by themethod of this invention may be described as:

Ln (0 .8 :RE, where x l or 0, where RE represents the following group ofelements:

Tb Terbium Sm Samarium Dy Dysprosium Ho Holmium Er Erbium Tm Thulium PrPraseodymium Eu Europium Gd Gadolinium Nd Neodymium; and where Lnrepresents the following group of elements: La Lanthanum Lu Lutecium YYttrium Gd Gadolinium and solid solutions of one or more of these.

Whereas the foregoing description of the invention has been madeprimarily in the context of rareearthactivated rare earth oxysulfidephosphors, it can be seen from the above generalized expression Ln (05,) :RE that 1: may equal 0, in which case the sulfur constituent dropsout. Thus, the invention in its most general conception, encompassesrare earthactivated rare earth oxides, as well as oxysulfides.

Further, as briefly noted above, whereas the emission manifolds mostsuitable for the selection of lines for comparison are the D and Dmanifolds for the europium activator, if other of the above-listedactivators are employed, other emission manifolds may be more suitable.In selecting the most suitable emission manifolds and intro-manifoldlines for a given activator, the following considerations areimportant: 1) the relative intensity of the emission manifold and itslines; 2) its overlap with other emission manifolds and the availabilityin the region of overlap of otherwise suitable lines from the differentmanifolds; and 3) the presence or absence of interfering emission linesor lines from foreign sources.

The invention is not limited to the particular details of constructionof the embodiments depicted and other modifications and applications arecontemplated. Certain changes may be made in the above described methodsand apparatus without departing from the true spirit and scope of theinvention herein involved and it is intended that the subject matter inthe above depiction shall be interpreted as illustrative and not in alimiting sense.

I claim:

1. A method for determining the emission color of the phosphor Ln (O,S,) :RE, where RE represents an element selected from the groupconsisting of terbium, samarium, dysprosium, holmium, erbium, thulium,praseodymium, europium, gadolinium and neodymium, and where Lnrepresents an element selected from the group consisting of lanthanum,yttrium, gadolinium and lutecium and solid solutions of one or more ofthese, comprising:

exciting the phosphor to cause light emission;

detecting the intensities of predetermined spectral lines in theemission spectrum of the excited phosphor; and

comparing the relative intensities of the detected lines to derive anindication of the emission color of the phosphor.

2. The method defined by claim 1 wherein the intensity peak heights ofthe predetermined emission lines are detected and compared.

3. A method for determining the emission color of a rare earth-activatedrare earth oxysulfide phosphor, comprising:

exciting the phosphor to cause light emission;

detecting the intensities of predetermined spectral lines in theemission spectrum of the excited phosphor; and

comparing the relative intensities of the detected lines to derive anindication of the emission color of the phosphor.

4. The method defined by claim 3 wherein said phosphor is selected fromthe group of phosphors consisting of europium activated yttriumoxysulfide, gadolinium oxysulfide, lutecium oxysulfide, lanthanumoxysulfide and solid solutions of one or more of these.

5. The method defined by claim 4 wherein said predetermined spectrallines comprise at least one line each from the manifold of linesassociated with D and D transitions.

6. The method defined by claim 3 wherein the intensity peak heights ofthe predetermined emissions are detected and compared.

7. A method for determining the emission color of a phosphor selectedfrom the group consisting of Y O S- :Eu, La O S:Eu, GD O S:Eu and Ln OS:Eu and solid solutions of these, comprising:

exciting the phosphor with ultra-violet irradiation to cause lightemission;

detecting the intensity peak height of predetermined spectral lines inthe emission spectrum of the excited phosphor, said lines comprising atleast one each associated with the D and D manifolds; and

comparing the relative intensity peak height of the detected linesassociated with the D and D, manifolds to derive an indication of theemission color of the phosphor.

8. The method defined by claim 7 wherein said predetermined spectrallines are proximate in the emission spectrum of the said phosphor.

9. A method for determining the emission color of europium-activatedyttrium oxysulfide phosphor, comprising:

exciting the phosphor with ultra-violet irradiation to cause lightemission; detecting the peak intensities of predetermined spectral linesin the emission spectrum of the excited phosphor, said lines comprisingat least one each associated with the D and D, manifolds; and

comparing the relative intensity peak heights of the detected lines inthe D. and D, manifolds to derive an indication of the emission color ofthe phosphor.

10. The method defined by claim 9 wherein said predetermined spectrallines are proximate in the emission spectrum and have correspondingintensity peak heights.

11. The method defined by claim 10 wherein said emission lines areassociated with the D F and D JF transitions.

12. The method defined by claim 11 wherein said predetermined emissionlines comprise the D F line and one of the multiple lines associatedwith the D, F transitions.

13. A method for determining the concentration of the activator in arare earth-activated rare earth oxide or oxysulfide phosphor,comprising:

exciting the phosphor to cause light emission; detecting the intensitiesof predetermined spectral lines in the emission spectrum of the excitedphosphor; and comparing the relative intensities of the detected linesto derive an indication of the activator concentration in the phosphor.

14. The method defined by claim 13 wherein said phosphor is selectedfrom the group of phosphors consiting of europium-activated yttriumoxysulfide, gadolinium, lanthanum oxysulfide and solid solutions of oneor more of these.

15. The method defined by claim 14 wherein said predetermined spectrallines comprise at least one line each from the family of linesassociated with D and D transitions.

16. The method defined by claim 13 wherein the in tensity peak heightsof the predetermined lines are detected and compared.

17. A method for determining the europium concen- I tration in aphosphor selected from the group consisting of Y O S:Eu, La o szEu, Gd OS:Eu and Lu O- S- :Eu and solid solutions thereof, comprising:

exciting the phosphor with ultra-violet irradiation to cause lightemission; detecting the intensity peak height of predetermined spectrallines in the emission spectrum of the excited phosphor, said linescomprising at least one each associated with the D and D, manifolds; and

comparing the relative intensity peak height of the detected linesassociated with the D and D, manifolds to derive an indication of theeuropium concentration in the phosphor.

18. The method defined by claim 17 wherein said predetermined spectrallines are proximate in the emission spectrum of the said phosphor.

19. The method defined by claim 17 wherein said predetermined emissionlines comprise the B E, line and one of the multiple lines associatedwith the D P transitions.

20. A method for determining the europium concentration ofeuropium-activated yttrium oxysulfide phosphor, comprising:

exciting the phosphor with ultra-violet irradiation to cause lightemission; detecting the peak intensities of predetermined spectral linesin the emission spectrum of the excited phosphor, said lines comprisingat least one each associated with the transitions B and D,; and

comparing the relative intensity peak height of the detected lines inthe D and D transitions to derive an indication of the europiumconcentration in the phosphor.

21. The method defined by claim 20 wherein said predetermined spectrallines are proximate in the emission spectrum and have correspondingintensity peak heights.

22. The method defined by claim 21 wherein said emission lines areassociated with the D '"F and D F transitions.

2. The method defined by claim 1 wherein the intensity peak heights ofthe predetermined emission lines are detected and compared.
 3. A methodfor determining the emission color of a rare earth-activated rare earthoxysulfide phosphor, comprising: exciting the phosphor to cause lightemission; detecting the intensities of predetermined spectral lines inthe emission spectrum of the excited phosphor; and comparing therelative intensities of the detected lines to derive an indication ofthe emission color of the phosphor.
 4. The method defined by claim 3wherein said phosphor is selected from the group of phosphors consistingof europium activated yttrium oxysulfide, gadolinium oxysulfide,lutecium oxysulfide, lanthanum oxysulfide and solid solutions of one ormore of these.
 5. The method defined by claim 4 wherein saidpredetermined spectral lines comprise at least one line each from themanifold of lines associated with 5D1 and 5D0 transitions.
 6. The methoddefined by claim 3 wherein the intensity peak heights of thepredetermined emissions are detected and compared.
 7. A method fordetermining the emission color of a phosphor selected from the groupconsisting of Y2O2S:Eu, La2O2S:Eu, GD2O2S:Eu and Ln2O2S:Eu and solidsolutions of these, comprising: exciting the phosphor with ultra-violetirradiation to cause light emission; detecting the intensity peak heightof predetermined spectral lines in the emission spectrum of the excitedphosphor, said lines comprising at least one each associated with the5D0 and 5D1 manifolds; and comparing the relative intensity peak heightof the detected lines associated with the 5D0 and 5D1 manifolds toderive an indication of the emission color of the phosphor.
 8. Themethod defined by claim 7 wherein said predetermined spectral lines areproximate in the emission spectrum of the said phosphor.
 9. A method fordetermining the emission color of europium-activated yttrium oxysulfidephosphor, comprising: exciting the phosphor with ultra-violetirradiation to cause light emission; detecting the peak intensities ofpredetermined spectral lines in the emission spectrum of the excitedphosphor, said lines comprising at least one Each associated with the5D0 and 5D1 manifolds; and comparing the relative intensity peak heightsof the detected lines in the 5D0 and 5D1 manifolds to derive anindication of the emission color of the phosphor.
 10. The method definedby claim 9 wherein said predetermined spectral lines are proximate inthe emission spectrum and have corresponding intensity peak heights. 11.The method defined by claim 10 wherein said emission lines areassociated with the 5D0 -> 7F0 and 5D1 -> 7F3 transitions.
 12. Themethod defined by claim 11 wherein said predetermined emission linescomprise the 5D0 -> 7F0 line and one of the multiple lines associatedwith the 5D1 -> 7F3 transitions.
 13. A method for determining theconcentration of the activator in a rare earth-activated rare earthoxide or oxysulfide phosphor, comprising: exciting the phosphor to causelight emission; detecting the intensities of predetermined spectrallines in the emission spectrum of the excited phosphor; and comparingthe relative intensities of the detected lines to derive an indicationof the activator concentration in the phosphor.
 14. The method definedby claim 13 wherein said phosphor is selected from the group ofphosphors consisting of europium-activated yttrium oxysulfide,gadolinium, lanthanum oxysulfide and solid solutions of one or more ofthese.
 15. The method defined by claim 14 wherein said predeterminedspectral lines comprise at least one line each from the family of linesassociated with 5D1 and 5D0 transitions.
 16. The method defined by claim13 wherein the intensity peak heights of the predetermined lines aredetected and compared.
 17. A method for determining the europiumconcentration in a phosphor selected from the group consisting ofY2O2S:Eu, La2O2S: Eu, Gd2O2S:Eu and Lu2O2S:Eu and solid solutionsthereof, comprising: exciting the phosphor with ultra-violet irradiationto cause light emission; detecting the intensity peak height ofpredetermined spectral lines in the emission spectrum of the excitedphosphor, said lines comprising at least one each associated with the5D0 and 5D1 manifolds; and comparing the relative intensity peak heightof the detected lines associated with the 5D0 and 5D1 manifolds toderive an indication of the europium concentration in the phosphor. 18.The method defined by claim 17 wherein said predetermined spectral linesare proximate in the emission spectrum of the said phosphor.
 19. Themethod defined by claim 17 wherein said predetermined emission linescomprise the 5D0 -> 7F0 line and one of the multiple lines associatedwith the 5D1 -> 7F3 transitions.
 20. A method for determining theeuropium concentration of europium-activated yttrium oxysulfidephosphor, comprising: exciting the phosphor with ultra-violetirradiation to cause light emission; detecting the peak intensities ofpredetermined spectral lines in the emission spectrum of the excitedphosphor, said lines comprising at least one each associated with thetransitions 5D0 and 5D1; and comparing the relative intensity peakheight of the detected lines in the 5D0 and 5D1 transitions to derive anindication of the europium concentration in the phosphor.
 21. The methoddefined by claim 20 wherein said predetermined spectral lines areproximate in the emission spectrum and have corresponding intensity peakheights.
 22. The method defined by claim 21 wherein said emission linesare associated with the 5D0 -> 7F0 and 5D1 -> 7F3 transitions.